Conductive coating materials are used to obtain a conductive coating (also referred to as conductive films herein). Most conventional conductive coating materials are those that use a colored conductive pigment (mainly black). Because the conductivity of such conductive pigments conventionally used is low, the amount of the conductive pigment added is required to be increased for improvement of the conductivity of coating. Because of the deep color of the conductive pigment, if added in high amount, the resultant coating material itself will be deeply colored and not transparent. For this reason, it was considered difficult to produce a coating higher in the conductivity and also transparency.
As for a coating material to obtain a highly transparent conductive coating, a coating material using indium oxide is known. However, the coating material using indium oxide has problems in that the indium oxide is expensive and that there is limitation in the amount of the indium oxide resource.
Thus, an electromagnetic shielding body is reported which is characterized in that a transparent conductive layer containing ultra-fine conductive fibers is formed on at least one side of a substrate, the ultra-fine conductive fibers are dispersed while in contact with each other without aggregation and the conductive layer has a surface resistivity of 105Ω/□ or less (Patent Document 1). However, a coating liquid for forming the conductive layer prepared by dispersing ultra-fine conductive fibers in a solution of a binder and dissolved in a volatile organic solvent, has a problem related to a volatile organic compound (hereinafter, referred to as “VOC” herein) from the viewpoint of environmental safety.
In order to solve the environmental safety problems, water is the most suitable solvent that can be used to reduce VOCs. Thus, we added a resin for aqueous coating material, as a binder, to a system in which water is used as solvent and a carbon nanotube is dispersed. As a result, significant aggregation occurred. Such a coating liquid with the occurrence of significant aggregation cannot be used for formation of coating.                Patent Document 1: Japanese Laid-open Patent Publication No. 2004-253796 (pp. 1 to 13)        